Revision of the Bivalvia from the Upper Jurassic Reuchenette Formation, Northwest Switzerland — Ostreoidea Author Koppka, Jens text Zootaxa 2015 3927 1 1 117 journal article 10.11646/zootaxa.3927.1.1 c9f96009-d3d4-4977-9cd5-6004214d1036 1175-5326 288034 42B56D11-9B18-4FCC-B632-30A46AB0205C Genus Nanogyra Beurlen, 1958 Type species . Gryphaea nana J. Sowerby, 1822 , p. 114, pl. 383 (left figure); BM 43340c, Kimmeridge Clay, England . Diagnosis (modified from Stenzel 1971 , p. N1121). Thin-shelled, inequivalve. Outline suborbicular, subtrigonal, elliptical, or ovate to comma-shaped (virguliform of authors); always opisthogyrate, degree of spirality variable. Left valve moderately convex to globular, smooth or with antimarginal riblets, rarely with small plicae; RV overall slightly concave or convex, with sharp, curved anterior carina. Posterior ligament bourrelet reduced in length, usually forming a ridge with the dorsal margin during early growth stages. Chomata known since Bathonian [see below, N. ( P. ) reniformis (Goldfuss, 1833) (b)]. Microstructure largely compact foliate some small chambers may be present close to the umbo and shell margin, complex cross-foliation common. Right valve with outer, coarsely prismatic layer ( Siewert 1972 , p. 19; Malchus 1990 , p. 109; Malchus & Aberhan 1998 , p. 629). Most species do not exceed 3 cm in largest diameter, but for some larger species exceptional specimens may reach a height of up to 7 cm . Remarks . The present diagnosis deliberately excludes? N. ( Nanogyra ) auricularis (Goldfuss, 1833) (b) as described in Malchus & Aberhan (1998) . The species has an unusual large size ( ca. 10 cm ), numerous large chambers, and a tendency to become uncoiled reaching a ligament area height of up to 4 cm . It is equally unclear whether the specimens from Europe and those from Chile belong to the same species. Malchus & Aberhan (1998) hypothesized that it represents a different genus.